Theme 1: Theory of science

What does Russell mean by "sense-data" and why does he introduce this notion?

According to Russell (The Problems of Philosophy, 1912) an object cannot be immediately known to us. We can only know an object through sings that we perceive about this object, signs that are associated to it. Russell defines “sense-data” as the things that we are immediately aware of, such as colours, smells, sounds, roughness etc of an object, while the experience of immediately being aware of those things is called sensation.

“Sense-data” depend on the way that we perceive them, on our senses. But, regardless of how much “sense-data” depend on us, their occurrence is a sign that exists independently of us. Our conception of sense-data depends on the relationships between us and the object. The important thing is that there is an object, regardless of its nature.

The reason why Russell introduced this notion is related to the fact that we cannot immediately know an object; if there is any. Our knowledge on the object comes from conclusions based on our immediate awareness- the “sense-data”. Russell introduced this notion to answer the question of whether this object really exists. And if there is such an object, what sort of object could it be?

What is the meaning of the terms "proposition" and "statement of fact"? How does propositions and statement of facts differ from other kinds of verbal expressions?

A proposition is a statement about a thing based on a judgement or a belief and it could be of the form “X is Ψ”. The same proposition could be said in different ways, e.g. we can use a name or words to describe a person in a proposition.

Russell underlines that the “proposition” should be composed of constituents with which we are acquainted. According to one example provided in the book, “two plus two equals four” is a “proposition”. Based on a priori knowledge, we know that two plus two will always give four. This is true. It is a fact. But whether it is a statement of fact or not depends on the situation.

So, “propositions” and “statements of facts” differ from other kinds of verbal expressions in the sense that they state something about the truth.

In chapter 5 ("Knowledge by Acquaintance and Knowledge by Description") Russell introduces the notion "definite description". What does this notion mean?

There are two types of knowledge: “knowledge of things” and “knowledge of truths”. This chapter is about the “knowledge of things” and this type of knowledge is further distinguished into “knowledge by acquaintance” and “knowledge by description”. The latter is about our knowledge concerning things that we are not acquainted with.

When talking about “knowledge by description”, Russell means any phrase of the form ‘a so-and-so’ or ‘the-so-and-so’. The author calls the phrase of the form ‘a so and so’, e.g. ‘a man’, as an “ambiguous description”, while the phrase of form ‘the-so-and-so’ (in the singular), e.g. ‘the man with the iron mask’ is defined as “definite description”. So, knowledge by definite description concerns things that we are not acquainted with, but we know that there is an object/thing answering to that definite description.

 

In chapter 13 ("Knowledge, Error and Probable Opinion") and in chapter 14 ("The Limits of Philosophical Knowledge") Russell attacks traditional problems in theory of knowledge (epistemology). What are the main points in Russell's presentation?

Russell discusses the difference between knowledge, error and probable opinion and he comments that the biggest part of what we consider as knowledge is probable opinion.

He argues that a true belief cannot be considered as knowledge. 

Part of his critique was about fragmentary and relational character of things. Russell criticizes the notion of the nature of the thing, which seems to mean all truths about a thing. This is not the case- the truth about a thing is not part of the thing itself. According to this reasoning we would never be able to know a thing’s true nature unless we know all the things’ relations to other things in the universe. We may have knowledge of a thing by acquaintance and acquaintance does not logically demand a knowledge of all its relations.

Building on Cantor and other mathematicians, Russell also attacks the philosophical arguments that tended to show the impossibility of infinite collections in the universe. According to him, the reasons for considering space and time as unreal are inoperable. Russell explained that there is a limit to our knowledge from experience on what exists; but no such limit exists in our knowledge by description (about things that we cannot have direct experience). He appears to be optimistic when saying that there are now new opportunities in knowledge.